Directive antenna system



June 24,- 1930. 7 c. R. ENGLUND 4 1,768,239

DIRECTIVE ANTENNA SYSTEM Filed July 8, 1925 p Patented June 24, 1930ATE'r FFEQE CARL R. ENG-LUND, 0F FREEI-IOLD, NEW JERSEY, ASSIGNOR T0WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., ACORPORATION OF NEW YORK DIRECTIVE ANTENNA SYSTEM Application filed July8,

To approach as closely as possible the ideal, so far not closelyapproximated inpractice, of a unidirectional receiving system;

To elficiently receive radio signals from a desired direction to thesubstantial exclusion of signals coming from a predetermined undesireddirection.

To efliciently receive at a station of a two- Way radio communicationsystem, signals from a cooperating distant station Without interferencefrom Waves radiated from the local transmitting station.

To achieve each and all of the above objects Without sacrifice ofprotection against strays or, in a somewhat broader sense, to achieveeach and all of the above objects and concomitantly to substantiallyprevent interference due to strays both from the desired direction andfrom other directions.

The Word strays is used here and throughout the specification andclaims, as in approved modern texts, to comprehend all signal simulatingphenomena not falling Within the category of signals, and therefore toinclude phenomena having artificial, as Well as natural origin. It isintended specifically to include both static and atmospheric.

An embodiment of the present invention is incidentally disclosed but notclaimed in U. S. Patent 1,668,?57, granted May 8, 1928, and assigned tothe American Telephone and Telegraph Company.

A specific object of the invention is to improve the operation of longantennae known as Beverage or Wave antenna, and in particular to improvethe methods of eliminating one or more of the minor lobes of its polarreception diagram, the presence of which lobes tends to cause theantenna to be merely preponderantly, instead of strictly,unidirectional.

By the improved means of this invention, the elimination is accomplishedWithout 1925. Serial No. 42,128.

adding, to a harmful extent, new areas to the reception diagram. Thepresence of these additional areas Would connote an increasedsusceptibility to the influence of strays, a susceptibility that ismeasured both by the size of the area and its angular extent. Inaccordance With prior practice, as represented by the practice of theRadiov Corporation which developed this type of antenna and is itsprincipal user, the Wave antenna is in effect arranged for simultaneousoperation in the two opposite axial directions, so as to have similarbut relatively reversed reception diagrams. After adjustment to providethe proper equality relation of the ordinates of the respective diagramscorresponding to a certain direction of interfering Waves, the currentsdue to Waves incident upon the antenna are superposed in the receivingcircuit. It is apparent that this prior method is inherently adapted forthe elimination of the axial minor lobe only since the receptiondiagrams must be unvaryingly 180 degrees apart. The lateral lobes, orcertain of them, can be eliminated only by relatively enormouslyincreasing the size of the reception diagram representing thecompensating circuits With the production of a corresponding enormouslyincreased additional reception area along the reverse axis.

By the method of the present invention, any selected lobe Whatever canbe eliminated with the same facility as the axial or any other lobe, andwith no sacrifice of protection against strays.

Specifically, in the method of the present invention, the compensatingWave is picked up by an entirely independent antenna, the receptiondiagram of Which has sucha configuration as to readily lend itself tocombination With the corresponding diagram of the principal antenna, ifsuperposed in a particular angular relation, to produce the desiredresultant diagram. This independent or aux- 9 "inthe appended claims.

equal and opposed over the region of the lobe to be eliminated.

Because the Wave antenna is normally so.

nearly unidirectional, the auxiliary antenna 'may be relatively small,since the area of its reception diagram is of the order of that of theparticular minor lobe 'tobecompe'nsated or eliminated. Although perhapsa substantially unidirectional auxiliary antenna tvouldfoln theoreticalchnsiderations, be preferr'edfit has been found that a-simple-dirigibleloop, having a bidirectional reception diagram resembling theshapeofa'figure's Well answers every practical purpose. By means ofthisinvention any one of the minor "lobes'of the receptiondiagram'of theprincipal antenna 'may be substantially Wholly eliminated. Withith'eproduction of a'very small additional reception area which 'Will bedistributed partly in the general direction of that lobe and partly insubstantially the reverse'direction. lf under special conditrons,the'add tronal expense would be gust1fiecl,the ordinary dirigible loopcould be re placed by a dirigiblevantenna having a uniand method ofoperation Will best be understood by reference'to the following descrip-'tion' taken in connection with the adcon1panyingdrawings in which:

Fig. lisa circuit'di'agram of one embodiment of the system of'theinvention.

Figy2is apo-lar reception-diagram illustrating the operatingcharacteristics "of the Wave "antenna which constitutes a portion of"the-system of Fig. 1.

='Fig.3-is'"a:p'olar reception diagram illustrating the operatingcharacteristics of the loop-antenna Whichc'onstitutes another portion ofthe system of Fig. 1; and

I Fig. iis a polar reception diagram illustratin'g'the operatingcharacteristics of the system of Fig. l as a Whole including both an aei 7 Before entering on the description of the specific arrangement ofthe invention, Which make useof any one of several forms of Wave"antenna cir"c'uits,'the general theory of the operation of wave antennaewill be delop'ed. This plan,"as providing a"b'aclrgroimdffor'thespecific invention tliat'is to b'eclesci'i bed,'tvill tend to aid oneinloolring back of the specific disclosure illustrated in the drawingto'determine the Teahnature and extent 'of the invention.

' he following references comprise in their disclosures substantiallyall of-the learning and practice in this art available to the public upto this time. They, or some of them, may be studied to advantage inconnection With this specification:

(1) A paper by Beverage, Rice, and Kello rinted in three arts in theJournal 7, 1921, 1,434,984., November 7," 1922, 1,434,-

985, November 7, 1922 and 1,43%,986, Novem-- bel' 7, 1922.

I Kellogg U. S. Patent 1,387,339, March rrwvave' antenna'may besimplyany substantially straight current conducting circuit,'having alengthof the'ord'er of the Wave length -'of' the ether Wave, extending'substantially horizontally, along which Wave energy impressed" upon itmay be p'ropagated at a velocity comparable with that of the same Wavein ether. lhe last requirement maybe satisfied by inserting condensersin seri'esiat uniform intervals'throughoutthe length of the antenna,which may otherwisehave the form of an ordinary transmission line of oneor more conductors grounded at each end. The same effect, that ofincreasedvelocity' of propagation, may be se'cured'by insertinginductances betweaentheantenna and ground. a I lnaccordance With themost easily explainable theory of 01 eration,a Wave generated at one endof the antenna,.hereinafter called the near end, by an ethervvave'whichtravels in the direction of extension of the antenna, is propagatedalong tl e antenna. The ether Wave also generates awave in each of theother elemental lengths into which the antenna may be considereddivided, and theseWaves are similarly propagated along the antenna. Theefiect,'pra ctically, is that the Wavev generated at the end of theantenna absorbs energy from'theaccompanying ether Wave and thereforeincreases i-n amplitude as it progresses along the antenna, attaining amaximum at the opposite end, hereinafter called theremote end, Where thereceiver is locatec. By parity of reasoning there WOlllCl'lOG no energyat the receiving end absorbed from a Wave proceeding in the oppositedirection, although an additional receiver at the opposite endcould'efi'ectively'receive sucha Wave. In order that the above operationmay not be complicated by reflection effects, and accordingly so thatthe unidirectional character of the antenna may be preserved, the groundlead at the end opposi'te to the receiver, and thereforeat bothends iftwo receivers are to be used, maybe caused to have'an impedance F equalto the surge impedance of the antenna. Meanssuch asthis have, 1npractice, been sufi icient to nearly but not quite eliminate the axial'minor' lobe. Instead of placing the receiver at the remote end, as inthe ground lead, a reflection transformer can be placed in this groundlead 1f a t wconductor antenna 1s used and the antenna can then be usedlike an ordinary transmission line (current flow ing in oppositedirections in the two conductors) to transmit the energy back to thenear end where the receiver may be placed. This permits the elementwhich determines the surge impedance to be placed near the re-' ceiverwhere the impedance of the element can antenna continues to build upuntil limited only by the antenna losses, that is, the benefits of anextra long antenna can be secured by high velocity (so long as it is nothigher than that of light) and low attenuation. if the two velocitiesare not the same, there will be a cyclical variation of amplitude of thewave along the antenna as the relative phases of the two waves vary.through successive conditions of coincidence and opposition, and anextra long antenna is not of advantage, so far as it affects the maximumsignal strength. It has been found that, in general, the directivity asdetermined principally by the area of the axial minorlobe increases asthe velocity of propagation approaches the velocity of light (compareFigs. 35, 36, and 39 of the above mentioned American Institute paper).The decrease in the width of the major lobe as the propagation velocitydecreases is favorable but is not suiiicient to compensate for the moreimportant efiect of change of area of the axial minor lobe. Also, asappears from a comparison of Figs. 35, 37 and 38 of the same paper thedirectivity improves somewhat as the length of antenna increases principally on account of the decrease in the width of the major lobe. Inpractice, it has been found that in order to obtain maximum strength ofsignals the length of the antenna should be at least half the length ofthe ether wave and preferably several times this length.

It should be noted that, if the antenna design is such that thepropagation velocity is not equal to the velocity of light, the antennanecessarily must have a certain frequencyvelocity characteristic.Practical use can be made of this characteristic in order to obtainfrequency, as well as directional, selectivity. This may be done bypositioning receivers, intended'for reception of waves of differentfrequencies, at different positions along the antenna. Similarly thismethod of positioning the receivers may be used to avoid the effect ofsystematic stray interference. F or the purposes of this invention thevelocity should be as nearly that of light as possible and theattenuation should be assmall as possible.

The above discussion treats of the mode of operation when an ether waveis incident on the antenna in the direction of its axis. The describedmode of operation accounts for the presence of a pronounced major lobeof the reception diagram. Considering now the effects of ether wavesincident on the antenna at an angle to its axis, it is evident that oneof the effects is to shorten the distance the ether wave has to travelbetween its incidence on successive elemental lengths as compared withthe case where the wave travels in a cothese differences in distance,translated into differences in phase, have simple integral multiplerelations that result in a reenforcenientsubstantially like that wherethe ether waves and antenna waves are travelling along the antenna inparallel. This at least qualitatively explains the existence of thelateral minor lobes.

The number, size and angular relation of these lobes can be caused todiifer greatly by adjustments of the length, propagation velocity, andattenuation of the antenna. For example if the antenna is an integralmultiple of half the wave length and if the propagation velocity equalsthat of light (a coincidence of conditions diflicult to realize inpractice) the axial minor lobe Will be absent; The polar diagramillustrated in Fig. 2 is as nearly typical as any and is the one assumedto result from the operation of the system of Fig. 1 now to bedescribed. Except perhaps as to the relative values of the ordinates, itis the same as Fig. of the American Institute paper above mentioned.

The foregoing explanation should bekept in mind in considering thefollowing description of a specific embodiment. Referring to Fig. l, theantenna 1 is of thewave type and, as used in this system, receives mostefiiciently waves coming from the right. The antenna comprises atwo-conductor line extending from the near end (near with respect to theether waves) to the reflection transformer 2.

The ground circuit at the near end contains. impedance 3 adjusted toequal the surge impedance of the antenna to prevent reflection of wavespropagated along the antenna from the other (the remote) end. Thesewaves, if reflected, would be superposedonan'd be indistinguishablefrom, the desired waves. The other end is grounded through thereflection transformer 2 which transduces the energy there received backto the antenna which ac cordingly serves as an ordinary transmissionline (currents flowing in" opposite directions in the two conductors)ttT-hTHHSHHhtllQ'11- ergy to'the-near' end! If the antenna were not soused, the receiver could, and conven ie'ntlywould, be placed inthe"ground leadat the remote end This ground lead does not contain anelement the primary function of whichis to match the surgeinipedance,since the'refiection transformer is designed toeffectthisresult. 7 a

The disclosure of the antenna itse'ltis diagrammatic only.

7 may actually consist simply of a two-conductional forms now known andmay be'causedtor line, if the'distributed ind'uctanceand capacity'aresmall enough to give apropagation'velocity comparable with thatoflight,or such a line varied by the inclusion ofseries-condei'isers or shuntinductances, or both, asha's been explained.

At the near end, the desired energy is again transducedi by transformer4 to circuit 5.

The two halves of the'primary of transformera are related to thesecondary winding,

and to each other, in such a manner tliatma gnetic-efifects resultingfrom undesired wavespropagatedsimultaneously along both wires of the'an'tenna from the remote to the near end; are balanced out 111 43116secondary winding. That is, this balanced circuit arrangementpreve'ntssuch-undesired waves from directly affecting the receivingcircuits connected tocircuit 5,-whil'e the surge impedance element 3-prevents these waves from being reflected and thereby later enteringcircuit 5' through-transformer 4:. v I

The receiving circuits connected to the circuit 5 include an amplifierAM- and a radioreceiver RR. The amplifier, of course, may

be om-itted on occasion, andthe transformers 6 and 7, whereby energy istransferred to the relatedcircuits, may be replaced by well knownequivalents The radio receiver may comprise any one of the well knowncircuit arrangements in which the impressed modulated carrier wave isdemodulated to reproduce the low frequency modulatingcomponent, as radiotelephony,- or rectified to reproduce radio telegraphic signals. Thedemodulated component is impressed on low frequency circuit 8.Tllfi'ftidlO receiver include a filter, to eliminate the undesiredfrequency components resulting from demodulation so that only the lowfrequency signal currents are transmitted to circuit 8. V A; loopantenna 9, here diagrammatically illustrated, may be of any one of theconvento be dirigible also in accordance with conventional practice, .asby a simple rotatable mounting. Fig. 3 illustrates-the polar rec'eptiondiagram or a loop antenna, the axis drawn through thediameter of the twolobes corresponding to the direction of the plane of the loop. Sincethis direction can be va- Accordingly the antennajust the phase of thewavesderived from'the loop antenna sothat they are in opposite. phase tothose derived from the waveanenna, withrespect toth-e-waves incident onthe system frointhe directio'n corresponding to-tlielobe which istobeelim'ina tedl The pe t'eiitionicter functions to equate the amplitudesot-the two waves for-this direction.

In order that the function-of the-loop-antenna system" as related to thewave antenna system may be better understood, reference is made to Fig.i. In'thisfigure, polar di'agrams corresponding to Figs. 2- and 3 areshown respectively in-light full; an-dbrolren lines. The heavy fulllines illustrate there.- sultant polar reception diagram.-- This resultant diagram indicates the current im pressed upon the input of theradio receiver resulting from the superposition of: the two componentcurrents. The resultant diagram may be plotted, as it was in drawingthis fig-- ure, by superposing the two component dia grams, dividing thefield into as manylines representing directions as is practically pos--sible adding the ordina-tesof thetwo di'a grams for each line whiletaking into account the differences in phase laying oifthese differencevalues from the origin and along the same directions, and" connectingthepointsthusobtained. I

It is mentioned above that account must be tal'renof differences inphase. This results flOIIl' the tact that the phase of the current, atthe input of the radio receiver, derive'd froin the wave antennaprogressively varies with a corresponding variation of the angle of theincident waves with respect to thata-ntenna.

This variation of ph'a se is indicated directly by the quantities in thelast column of table HI or" the above" mentioned America-n Institutepaper, which assumes a set of conditions similar to those assumed here.There is no corresponding phase Variation for the loop antenna exceptwhere the rotating vector passes from an angle corresponding t'oone sideofthe plane of the loop to an angle corresponding'to the other side. Therelations of the two superposed currents can be" ob' tained very easilyby merely superposing a curve taken from the last column o'litable' IIIon a rectangular curve for the loop antenna, adjusting these curves asis practically'accomplished by phase shifting device= 10) u ntil thereis opposition of phase at thecent'er of the lobe to be eliminated andpicking 011' the corresponding diflerences of phase for the otherangles. The details of this method are not disclosed in the drawingsince they would tend to unnecessarily complicate it and because thequalitative relations, which are all that required to teach th essentialprinciples of the invention, are thought to be sufiiciently apparentwithout recourse to rigid geometrical methods of proof. The importantthing to notice is that, beginning with the central line of the minorlobe there are four substantially equally spaced angles at which thereis exact phase opposition and four symmetrically located intermediateangles at which there is phase coincidence.

For the assumed case, it was desired to eliminate the lobe indicated inFig. 2 as a. For example, this lobe might point in the general directionof the local transmitting circuit of a two-way radio telephone station,of which the circuits of Fig. 1 constitute the receiving circuits.

The loop antenna would be accordingly oriented to a position such thatthe combination of currents in accordance with the method explained inthe above paragraph results in as complete an elimination of this lobeas possible. The position of the polar diagram for the loop antenna inFig. 4 indicates the best position of this antenna to satisfy thiscondition.

The potentiometer 11 would also be adjusted so as to contribute to thesatisfaction of this condition. That it has been so adjusted in theassumed case is indicated by the equality of the ordinates of the twocomponent diagrams of Fig. i for a direction corresponding to the centerof the lobe. The resultant heavy full line diagram indicates that thelobe has been substantially eliminated.

The resultant diagram also indicates that very little additional areahas been produced. This area is indicated by that part or" the resultantdiagram outside of the diagram for the wave antenna, i. e. light fullline diagram.

In accordance with prior practice, the compensating wave would beobtained from the ground lead at the near end of the wave antennainstead of from a separate dirigible antenna. The compensating wavewould therefore be the wave resulting from the use of the antenna forwaves oppositely directed relatively to those called the desired wavesin the description of this invention. The polar diagram for thecompensating wave would be similar to that of Fig. 2 but relativelyreversed. It would be invariable in position with relation to thediagram for the desired waves. Accordingly, such a diagram could besuperposed on that of Fig. 2 in such a manner as to substantiallyeliminate the axial lobe b of Fig. 2, and this is its normally intendedfunction. However, if it were attempted to eliminate the lobe a, as bygreatly increasing the size of the compensating wave diagram, a strayarea of relatively large dimensions would be added to the polar diagramfor the antenna system.

l Vhat is claimed is:

l. A radio receiving circuit comprising in combination, a preponderantlyunidirectional receiving antenna, a directive dirigible antenna, saidantennae being of types such that the axes of their polar receptiondiagrams are relatively displaced as the dirigible antenna is moved,receiving apparatus, and means whereby electrical variations produced insaid antennae when adjusted so that the axes of their polar diagrams arerelatively displaced are superposed on said apparatus.

2. The combination recited in claim 1.in which the dirigible antenna isofthe unidirectional type.

3. The combination recited in claim 1 in which the dirigible antennacomprises a loop aerial, and means for rotating said loop about avertical axis.

4-. The combination recited in claim 1 in which'the unidirectionalantenna is a horizontal wave antenna.

5. The combination recited in claim 1 in which the unidirectionalantenna comprises a substantially horizontal wave conducting circuitgrounded at each end, having a substantially aperiodiccharacteristic, alength oi the order of the wave length of the waves incident thereon anda propagation velocity comparable with that oi ether waves, and in thatthe dirigible antenna comprises a loop aerial and means for rotating itabout a vertical axis.

6. In a directive radio receiving circuit, in combination, a waveantenna, comprising a substantially horizontal wave conducting circuitextending in the general direction of the source of radio waves which itis desired to receive, said circuit being substantially aperiodic,having a wave length of the order of the waves incident thereon and apropagation velocity comparable with that of ether waves, a circuitconnecting the end nearest the distantsource with ground and having animpedancesubstantially equal to the surge impedance of the conductingcircuit; a radio receiving apparatus; means for impressing on saidapparatus the waves propagated to the end of the wave antenna remotefrom said source; adirigible antenna comprising an aerial loop and meansfor rotating it about a vertical axis; and means for impressing thewaves receivedby said loop on sald apparatus in any desired phaserelation with respect to the propagated waves.

7. The method of eliminating a selected minor lobe of a polar receptiondiagram of a horizontal aperiodic antenna, using a horizontal aperiodicantenna and a rotatable loop antenna, which comprises rotating said loopantenna until the axis of its polar reception diagram substantiallycoincides With the axis of said minor lobe, receiving radio Wavesjointly with said antennae and super-posing the resultant Waves.

v8. The method using a directive horizontal aperiodic antenna and adirigible loop antenna, of receiving desired Waves from a directioncorresponding to the major lobe of the polar reception diagram of saidhorizontal aperiodic antenna, to the substantial exclusion ofinterfering Waves from a directionycorresponding to a selected minorlobe of said diagram, Which comprises orienting said loop antenna so asto most efficiently receive Waves from a direction corresponding to saidminor lobe, receiving the desired and interfering aves on saidhorizontal aperiodic antenna and compensating Waves on said loopantenna, and superposing all'of said Waves in such phase relation thatthe interfering Waves are substantially balanced out by saidcompensating aves. 7

9. A radio receiving circuit comprising incombination, a fixed,preponderantly unidirectional, receiving antenna, a "directive dirigibleantenna, said antennae being of types such that the axes oftheir polarreception diagrams are relatively displaced as the dirigible antenna is1noved,.receiving apparatus, and means whereby the electrical variationsproduced in said antennae are superposed on said apparatus. p

10. The combination recited in' claim 9, in Which'the dirigible antennais of a unidirectional type.

11. The combination recited in claim 9, in which the dirigible antennacomprises a loop aerial, and means for rotating said loop about avertical a'xi 12. The method of improving the directive receivingqualiJlQS of an antenna which is pre ponderantly unidirectional, using arotatable loopantenna, which comprises rotating said loop antenna untilthe axis of its polar 'rece'ption dia ram substantially coincides With aregion or the polar reception diagram of said unidirectional antennawhich it is desired to at least partially eliminate, receiving radioWaves jointly With said antennae, and superposing the resultant Waves.

In witness whereof, I hereunto subscribe my name this 7th day of -July,All). 1925. CARL R. ENGLUN D.

